Tubular heat exchanger with elastomeric outer sleeve



Sept. 10, 1968 D. N. CAMPBELL ,7

TUBULAR HEAT EXCHANGER WITH ELASTOMERIC OUTER SLEEVE Filed Dec. 30,-1966 INVENTOR wan, wflww M ATTORNEYS United States Patent 3,400,757TUBULAR HEAT EXCHANGER WITH ELASTOMERIC OUTER SLEEVE David NeilCampbell, Redditch, England, assignor to The Hymatic Engineering CompanyLimited, Redditch, Worcestershire, England, a company of Great BritainFiled Dec. 30, 1966, Ser. No. 606,294 Claims priority, application GreatBritain, Jan. 7, 1966,

854/66 5 Claims. (Cl. 165-134) ABSTRACT OF THE DISCLOSURE A heatexchanger comprising a finned t-ube helically wound round an inner tubewhich has an elastomeric sleeve shrunk round the finned helical tube andbulging inwards between its convolutions.

inner body comprising an inner tube in the form of a helix extendingsubstantially co-axially within the outer tube and provided with annulardisc-like heat-exchanging fine lying generally in planes containing theaxis, in which the outer body includes an elastomeric sleeve shrunkround and embracing the exposed edges of the fins and bulging inwardsbetween successive convolutions of the helix so as to constrain fluidpassing between the fins at their outermost points to remain in contactwith them for an appreciable distance.

Preferably one or each end of the elastomeric sleeve is sealed to arigid tubular header. Thus the header at each end may conveniently besecured to a single rigid outer protective tube enclosing and protectingthe elastorneric sleeve and sealed to it adjacent one or each of itsends. The sleeve may afford one or more annular ribs engaging the innersurface of the outer protective tube to form the seal or seals. It maybe desirable that the part, or each part, of the sleeve forming the sealwith the outer tube should be spaced longitudinally from the part whichis shrunk round the inner body.

The invention may be put into practice in various ways. A specificembodiment will be briefly described by way of example with reference tothe accompanying drawing, which is a fragmentary longitudinal sectionthrough the wall of a heat exchanger embodying the invention.

In the example the invention is applied to a heat exchanger of the typedescribed in the present applieants United States of America patentapplication Ser. No. 570,062, now abandoned. The heat exchanger isembodied in a cryogenic cooler, working on the principle of theJoule-Thomson effect, to effect heat exchange between fluid travellingfrom the atmospheric end to the cold end of the apparatus and fluidreturning in the opposite direction.

The heat exchanger is generally in the form of a straight tube and, inthe drawing the inner portion, in the region of the axis 9, is occupiedby other parts of the apparatus. The heat exchanger comprises an innertube 10 in the form of a helix coaxial with the apparatus. The helicaltube is provided with disc-like cooling fins 11 which accordingly liegenerally in planes containing the axis of the helix. The finned helicaltube is wound round a central axial tube 12 which is either providedwith a grooved former having a helical groove to receive and. locate theinnermost portions of the fins or (as shown) is provided with a helicalsingle start or two start winding of thread 13 for the same purpose.

In such an arrangement it has hitherto been customary to provide asimilar winding or windings of thread round the outer portion of thefinned helical tube, and fit a rigid metal outer tube round the outerthread winding, the outer thread winding serving both to eifect a sealwith the outer containing wall and to force the gas into more intimatecontact with the heat exchange area. In practice it is necessary toexercise close dimensional control over the effective outside diameterof the wound assembly to ensure a good fit with the outer wall.

In the arrangement in accordance with the present invention the outerwinding of thread is omitted, and instead a sleeve 15 of syntheticelastorneric material is placed over the finned helical tube and isshrunk in position. The sleeve is of a material such as irradiatedpolyvinyl chloride or irradiated polytetrafluoroethylene, which has theproperty that upon gentle heating it shrinks to conform closely to thesurface to which it is applied.

The elastomeric sleeve is in turn contained within an outer rigid metaltube 16 which protects it, .and, at its ends, carries headers 18 for theinlet and outlet of fluid. Headers 18 may be rigid circular ringschannel-shaped in cross-section with its flanges respectively secured toouter tube 16 and central tube 12. The headers are provided withapertures 19 to permit both insertion of coil 10 through the heatexchanger unit and, as may be located along the circumference of headers18, to permit fluid to flow past the fins 11. The elastomeric sleeve isprovided at its 'ends with external annular ribs 17 which form a sealwith the outer rigid tube 16. These ribs may if desired be spacedlongitudinally from the portion of the sleeve that is shrunk round thefinned helical inner tube.

The outer rigid tube 16 may be afforded by the inner wall of an outercontaining vessel such as a dewar vessel in which the assembly isremovably mounted. The arrangement allows the assembly to be readilyremoved from the container with its header and pipe connections.

It will be appreciated that the elastomeric sleeve bulges inwardsbetween successive convolutions of the helical finned tube, so as notonly to locate the: tube but also to constrain the fluid flowing pastthe outermost points of the fins to remain in contact with them for anappreciable distance. This eliminates the possibility that certainportions of the gas may flow from end to end of the heat exchanger whilehardly coming into contact with the fins of the inner tube.

What I claim as my invention and desire to secure by Letters Patent is:

1. A heat exchanger in a cryogenic cooler working on the principle ofthe Joule Thomson eifect including a generally tubular outer body and anelongated inner body comprising an inner tube in the form of a helixextending substantially co-axially within the outer tube and providedwith annular disclike heat-exchanging fins lying generally in planescontaining the axis, in which the outer body ineludes an elastomericsleeve shrunk round and embracing the exposed edges of the fins andbulging inwards between successive convolutions of the helix so as toconstrain fluid passing between the fins at their outermost points toremain in contact with them for an appreciable distance.

2. A heat exchanger as claimed in claim 1 in which at least one end ofthe elastomeric sleeve is sealed to a rigid header.

3. A heat exchanger as claimed in claim 2 in which 3 '4 headers at eachend are, secured to a single rigid outer References Cited protectivetube enclosing and protecting the elastomeric UNITED STATES PATENTSsleeve and sealed to it adjacent at least one of its ends. 2,643,8636/1953 Buschow 165 180 X 4. A heat exchanger as claimed in claim 3 inwhich the 3,326,015 6/1967 Webster 62 514 sleeve affords at least oneannular rib engaging the inner 5 FOREIGN PATENTS surface of the outerprotective tube to form the seal. 861 2/1961 Great Britain I 5. A heatexchanger as claimed in claim 2 in which at 938372 10/1963 GreatBritain:

least one part of the sleeve forming the seal with the outer rigid tubeis spaced longitudinally from the part 10 ROBERT Examinerwhich is shrunkround the inner body. A. W. DAVIS, Assistant Examiner.

